Oligomer solid acid and polymer electrolyte membrane including the same

Abstract

An oligomer solid acid and a polymer electrolyte membrane using the same. The polymer electrolyte membrane includes a macromolecule of oligomer solid acid having an ionically conductive terminal group at its terminal end and the minimum amount of ionically conductive terminal groups required for ion conduction, thus suppressing swelling and allowing a uniform distribution of the oligomer solid acid, thereby improving ionic conductivity. Since the number of ionically conductive terminal groups in the polymer electrolyte membrane is minimized and the polymer matrix in which swelling is suppressed is used, methanol crossover and difficulties of outflow due to a large volume are minimized, and a macromolecule of the oligomer solid acid having the ionically conductive terminal groups on the surface thereof is uniformly distributed. Accordingly, ionic conductivity is high and thus, the polymer electrolyte membrane shows good ionic conductivity even in low humidity conditions.

1 . An oligomer solid acid comprising: 
 (a) a main chain having a degree of polymerization of 10 to 70; and    (b) a side chain having the structure represented by Formula 1 bonded to a repeating unit of the main chain:     -E 1 - . . . -E i - . . . -E n   Formula 1   where each E i  included in E 1  through E n−1  is independently one of the organic groups represented by Formula 2 through Formula 6,                          where each E i+1  of Formula 4 through Formula 6 can be independently the same or different,    the number of E i+1  of the (i+1) th  generation bonded with E i  of the i th  generation is the same as the number of available bonds existing in E i ,    n is an integer in the range of 2 to 4 and indicates the generation of a branching unit; and    E n  is one of —SO 3 H, —COOH, —OH, and —OPO(OH) 2 .    
     
     
         2 . The oligomer solid acid of  claim 1 , wherein the repeating unit of the main chain is polystyrene, polyethylene, polyimide, polyamide, polyacrylate, polyamic ester, or polyaniline.  
     
     
         3 . The oligomer solid acid of  claim 2 , wherein the repeating unit of the main chain is the repeating unit of one of Formula 7 through Formula 9.  
       
         
           
           
               
               
           
         
       
     
     
         4 . The oligomer solid acid of  claim 1 , wherein the side chain is the chain of one of Formula 10 through Formula 15:  
       Formula 10 
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
       
       where R is one of —SO 3 H, —COOH, —OH, and —OPO(OH) 2 .  
     
     
         5 . The oligomer solid acid of  claim 1  having a molecular weight of 10,000 to 40,000.  
     
     
         6 . A polymer electrolyte membrane comprising at least one polymer matrix having an end group selected from the group consisting of —SO 3 H, —COOH, —OH, and —OPO(OH) 2  at the terminal of a side chain, and the oligomer solid acid of  claim 1  uniformly distributed through the polymer matrixes.  
     
     
         7 . The polymer electrolyte membrane of  claim 6 , wherein the polymer matrix is at least one polymer material selected from the group consisting of polyimide, polybenzimidazole, polyethersulfone, and polyether-ether-ketone.  
     
     
         8 . The polymer electrolyte membrane of  claim 6 , wherein the polymer matrix is a polymer resin represented by Formula 16:  
       
         
           
           
               
               
           
         
       
       where M is a repeating unit of Formula 17,  
       
         
           
           
               
               
           
         
       
       where Y is a tetravalent aromatic organic group or aliphatic organic group, and Z is a bivalent aromatic organic group or aliphatic organic group;  
       X is a repeating unit of Formula 18,  
       
         
           
           
               
               
           
         
       
       where Y′ is a tetravalent aromatic organic group or aliphatic organic group, Z′ is a tetravalent aromatic organic group or aliphatic organic group, j and k are each independently an integer in the range of 1 to 6, and R 1  is one of —OH, —SO 3 H, —COOH, and —OPO(OH) 2 ; and  
       m and n are each in the range of 30 to 5000 and the ratio of m to n is in the range of 2:8 to 8:2.  
     
     
         9 . A Membrane Electrode Assembly (MEA) comprising: 
 the polymer electrolyte membrane of  claim 6 ,    a cathode on a first side of the polymer electrolyte membrane and having a catalyst layer and a diffusion layer; and    an anode on a second side of the polymer electrolyte membrane and having a catalyst layer and a diffusion layer.    
     
     
         10 . A fuel cell comprising: 
 the polymer electrolyte membrane of  claim 6;     a cathode on a first side of the polymer electrolyte membrane and having a catalyst layer and a diffusion layer; and    an anode on a second side of the polymer electrolyte membrane and having a catalyst layer and a diffusion layer.